As an emerging star of 2D nanomaterials, 2D transition metal carbides and nitrides, named MXenes, present a large potential in various research areas owing to their intrinsic multilayer structure and intriguing physico-chemical properties. However, the fabrication and application of functional MXene-based devices still remain challenging as they are prone to oxidative degradation under ambient environment. Within this review, the preparation methods of MXenes focusing on the recent investigations on their thermal structure-stability relationships in inert, oxidizing, and aqueous environments are systematically introduced. Moreover, the key factors that affect the oxidation of MXenes, such as, atmosphere, temperature, composition, microstructure, and aqueous environment, are reviewed. Based on different scenarios, strategies for avoiding or delaying the oxidation of MXenes are proposed to encourage the utilization of MXenes in complicated environments, especially at high temperature. Furthermore, the chemistry of MXene-derived oxides is analyzed, which can offer perspectives on the further design and fabrication of novel 2D composites with the unique structures of MXenes being preserved. 

/pdf/recent-advances-in-oxidation-stable-chemistry-of-2d-mxenes-3bjy0lm7.pdf

Recent Advances in Oxidation Stable Chemistry of 2D MXenes

2D MXenes‐based nanoarchitectures are being actively explored for electrocatalytic water splitting because they possess physical and physiochemical properties that enhance catalytic activity toward the hydrogen evolution reaction and oxygen evolution reaction. This review systematically summarizes current strategies involved in defect engineering, including introducing atomic vacancies and active edges, and doping with metal and non‐metal atoms, which have been employed to achieve high‐efficiency MXenes‐based catalysts. The electronic structures, optimized adsorption/desorption energies of the intermediates, and possible catalytic mechanisms resulting from various defects are disclosed based on combined experimental results and theoretical calculations. Current challenges and future opportunities for the mechanistic investigation and practical application of defective MXenes‐based catalysts are proposed. This report aims to reveal the nature of defective MXenes electrocatalysts and to provide valuable guidelines for designing defective MXenes‐based nanoarchitectures for various catalytic reactions.

MXene Nanoarchitectonics: Defect‐Engineered 2D MXenes towards Enhanced Electrochemical Water Splitting

"Intrinsic" strategies for manipulating the local electronic structure and coordination environment of defect-regulated materials can optimize electrochemical storage performance. Nevertheless, the structure–activity relationship between defects and charge storage is ambiguous, which may be revealed by constructing highly ordered vacancy structures. Herein, we demonstrate molybdenum carbide MXene nanosheets with customized in-plane chemical ordered vacancies (Mo1.33CTx), by utilizing selective etching strategies. Synchrotron-based X-ray characterizations reveal that Mo atoms in Mo1.33CTx show increased average valence of +4.44 compared with the control Mo2CTx. Benefited from the introduced atomic active sites and high valence of Mo, Mo1.33CTx achieves an outstanding capacity of 603 mAh·g−1 at 0.2 A·g−1, superior to most original MXenes. Li+ storage kinetics analysis and density functional theory (DFT) simulations show that this optimized performance ensues from the more charge compensation during charge–discharge process, which enhances Faraday reaction compared with pure Mo2CTx. This vacancy manipulation provides an efficient way to realize MXene's potential as promising electrodes.

Vacancy manipulating of molybdenum carbide MXenes to enhance faraday reaction for high performance lithium-ion batteries

Numerical study of the effect of core geometry on the performance of a magnetostrictive transducer

Novel W-based in-plane chemically ordered (W2/3R1/3)2AlC (R = Gd, Tb, Dy, Ho, Er, Tm and Lu) MAX phases and their 2D W1.33C MXene derivatives

Structural, magnetic properties of in-plane chemically ordered (Mo2/3R1/3)2AlC (R = Gd, Tb, Dy, Ho, Er and Y) MAX phase and enhanced capacitance of Mo1.33C MXene derivatives

Zhaohui Chen

Papers

Structural, magnetic properties of in-plane chemically ordered (Mo2/3R1/3)2AlC (R = Gd, Tb, Dy, Ho, Er and Y) MAX phase and enhanced capacitance of Mo1.33C MXene derivatives

Effects of Co substitution for Fe on the structural and magnetostrictive properties of melt-spun Tb 0.2 Nd 0.8 Fe 1.9 ribbons

Coercivity evolution and suppressed thermally activated defects in diffusion processed Nd-Fe-B films